Charbonneau et al. in U.S. Pat. No. 6,063,464 have shown that incorporation of dianhydrosugar alcohols, such as 1,4:3,6-dianhydrosorbitol, hereinafter referred to by its trivial name “isosorbide”, can significantly raise the glass transition temperature (Tg) of terephthalate polyesters, such as poly(1,3-propanediol terephthalate). Poly(1,3-propanediol terephthalate), also known as poly(trimethylene terephthalate), is hereinafter abbreviated as 3GT. The relatively low glass transition temperature (Tg) of 3GT (˜45–50° C.) can lead to slight tackiness of the polymer when stored at high temperatures. An instance of this is sometimes evidenced on spools of fiber stored in warehouses in the hot weather of tropical countries. An increase in Tg lowers tack. Additionally, the low Tg leads to instability in spun fibers when stored under hot conditions. Partially drawn fibers under such storage conditions tend to undergo crystallization, forming a denser phase and causing fiber shrinkage, changes in denier and other undesirable changes in physical properties on storage. However, esterification of isosorbide with terephthalic acid or transesterification with dialkyl terephthalates involves the reaction of secondary hydroxyls and is slow compared with reaction of primary glycols such as ethylene glycol or 1,3-propylene glycol. This tends to lead to inefficient incorporation of the isosorbide. Using conventional condensation polymerization, this lower reactivity can lead to final polyesters that have lower molecular weights since unreacted isosorbides are detrimental to subsequent polymerization.
Adelman et al. U.S. Ser. No. 10/172,112, published as US 2003-0232960 A1, have described process improvements for the preparation of poly(1,3-propylene-co-isosorbide)terephthalate, hereinafter abbreviated as 3GIT. However, the secondary hydroxyl groups of the Isosorbide with the dibasic acid or its dialkyl ester have much lower reactivity than the corresponding reactivity of the primary hydroxyl groups of the 1,3-propane diol. This difference in reactivity has a number of effects, one of which is to lengthen the time needed for the solid phase polymerization step, a final procedure wherein the inherent viscosity of the polymer is increased to about 1.1 dl/g for good spinning properties.
It is desirable to prepare polyesters incorporating dianhydrosugar alcohols, such as 3GIT, with a low level of color and a Tg higher than the 45–50° C. Tg of 3GT, and, most importantly, both a low level of color and a higher Tg. Such improved properties aid in the use of such polyesters in shaped articles in many markets, including beverage bottles, film or sheet, fibers, monofilaments, and optical articles (e.g., compact discs or digital versatile discs).
It is particularly desired to increase the stability of shaped articles comprising polyesters having dianhydrosugar alcohols incorporated therein, particularly fibers and yarns such as partially oriented yarns, spun drawn yarns, and bulked continuous filament yarns, as well as staple fibers, to permit use of high speed spinning processes, without deterioration of the filament and yarn properties. It is further desired for these yarns to be useful in preparing products, such as textured yarns, fabrics and carpets, under the same or similar conditions to those used for yarns prepared at slower speeds.
The present invention provides shaped articles comprising ester-modified dicarboxylate polymers having such improved stability.